Spectral-zonal color reconnaissance system

ABSTRACT

Multiple images of a common scene are formed by exposure of photographic film primarily to separated zones of the actinic electromagnetic spectrum. The several film images are illuminated individually with lights of selected chromaticities. The chromaticity of the light illuminating at least one of the images is widely separated from the chromaticity associated with the corresponding exposing spectral zone for that image. The illuminated images are displayed in registration for evaluation.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of copending application Ser. No. 519,854, filedJan. 11, 1966, for "SPECTRAL-ZONAL COLOR RECONNAISSANCE SYSTEM", nowabandoned.

This invention relates to spectral-zonal color reconnaissance systemsand particularly to such systems adapted for aerial photographicreconnaissance sensing illumination from a plurality of separate zonesof the actinic portion of the electromagnetic spectrum, herein used toembrace the ultraviolet, the visible spectrum, and the near infrared.

A typical problem in aerial reconnaissance consists in the detection ofvehicles which have been painted to blend with the foliage and may beconcealed wholly or in part by cut foliage for purposes of additionalcamouflaging. Heretofore there have been proposed photograhicreconnaissance systems using spaced zones of the color spectrum to aidin analysis and interpretation of the photographs in accordance withestablished principles. These systems, in general, have employedcommercial multicolor photographic negatives, from which are madeordinary multicolor prints or transparencies. However, such systems havenot proved practical for aerial reconnaissance because of theprohibitive length of time for data reduction prior to viewing andevaluation. Such commercial multicolor films require extremely lengthlyprocessing times and complex chemical processing equipment. In additionto the time delay problem, they have not included provisions to permitalteration of the parameters, hue, brightness, and saturation, of thecolor image by viewer controls operated by the interpreter.

It is an object of the invention therefore, to provide a new andimproved spectral-zonal color reconnaissance system which obviates oneor more of the above-mentioned disadvantages and limitations of priorsystems of this type.

It is another object of the invention to provide a new and improvedspectral-zonal color reconnaissance system using a plurality of separatezones of the actinic portion of the electromagnetic spectrum.

It is another object of the invention to provide a new and improvedspectral-zonal color reconnaissance system requiring a minimum filmprocessing time, permitting rapid photographic analysis andinterpretation.

It is still another object of the invention to provide a new andimproved spectral-zonal color reconnaissance system including an opticalviewing apparatus capable of evaluating a plurality of spectral-zonalpositives in the following manners:

A. Monochrome presentation of individual spectral images for detailedstudy of the scene characteristics in each zone of the spectrum.

B. Presentation of conventional monochrome panchromatic positives bysuperposition of red, green, and blue spectral-zonal positives withoutusing color filters in the viewing system.

c. True color presentation utilizing the red, green, and bluespectral-zonal positives in an additive color system.

d. False color (camouflage detection) presentation utilizing arbitrarilyselected spectral-zonal positives in an additive color system.

In accordance with the invention, in a spectral-zonal colorreconnaissance system there is provided an optical viewing apparatus forevaluating a reconnaissance film including multiple images of a commonscene which have been exposed primarily to separated zones of theactinic electromagnetic spectrum, comprising means for illuminating thefilm images individually with white lights, means for selectively makingeffective any one or more of the illuminating means, means for alteringthe relative intensities of illumination of the viewed images, andoptical means for displaying the selected illuminated images forevaluation.

Further in accordance with the invention, in a spectral-zonal colorreconnaissance system there is provided an optical viewing apparatus forevaluating a reconnaissance film including multiple images of a commonscene which have been exposed primarily to separated zones of theactinic electromagnetic spectrum comprising means for illuminating thefilm images individually with lights of substantially the samechromaticities as their respective exposing spectra or with lights ofchromaticities substantially different therefrom, means for selectivelymaking effective any one or more of the illuminating means, and opticalmeans for displaying the selected illuminated images for evaluation.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription, taken in connection with the accompanying drawings, whileits scope will be pointed out in the appended claims.

Referring now to the drawings:

FIG. 1 is a perspective schematic view of a spectral-zonal color camerafor use in the system of the invention, while

FIG. 2 is a schematic perspective view of an optical viewing apparatusfor use in the system of the invention.

Referring more particularly to FIG. 1 of the drawings, there isrepresented a camera means for use in a spectral-zonal colorreconnaissance system embodying the invention. This camera includesmeans for individually exposing, in precise relative positions, discreteportions of a photosensitive film to a common scene by illumination ofseparated zones of the actinic electromagnetic spectrum to form multipleimages thereon. Specifically, the camera of FIG. 1 includes fourlens-filter combinations 11-14 designed individually to transmitradiation from the scene corresponding to any four zones of the actinicelectromagnetic spectrum from ultraviolet through near infrared. Forexample, lens-filter combination 11 may transmit energy in the blueregion from 4,000 to 5,200 A.; lens-filter combination 12 in the greenregion from 4,800 to 6,100 A.; lens-filter combination 13 in the redregion from 5,900 to 7,100 A.; and lens-filter combination 14 in theinfrared region from 7,100 to 9,000 A. These restrictions in spectralbandwidths can be accomplished by the use of standard commercial Wrattenfilters Nos. 47, 58B, 25, and 89B, respectively, although other filtersmay be used in applications where different spectral transmission bandsare desired. Since the lens-filter combinations 11, 12, and 13 havetransmission characteristics overlapping that of the infraredcombination 14, an infrared cutoff filter is preferably included in eachof the units 11, 12, and 13.

The camera represented in FIG. 1 is of the stationary film, moving lens,panchromatic type illustrated by way of example. It will be apparent,however, that other well-known types of aerial cameras may be employedsuch as the moving film panchromatic and frame and strip cameras. In thecamera of FIG. 1, a strip of film F passes from a supply spool 16 to atakeup spool 17 via a cylindrical vacuum platen 15. With such anarrangement, the lens-filter combinations 11, 12, 13, and 14 are mountedon a support 18 and mounted for oscillation about a pivotal shaft 19disposed coaxially with the cylindrical platen 15 for panoramicscanning. The lens-oscillating mechanism may be of conventional type andis omitted from the drawing for the sake of clarity.

In order to aid in accurate registration of positives made from imageson the film F, there is provided a reference flange or surface 20,against which the film is lightly indexed by means of a roller 21mounted on a light spring 22. In contrast to the elaborate processingrequired in making multicolor positive prints or transparencies from amulticolor exposed negative, the latent images on the exposed monochromefilm F may be developed in situ, using any of a number of availabletechniques such as a saturated hydrophyllic layer, a porous plastic web,or conventional wet processing. The time required in processing such apositive transparency is a small fraction of that for processingmultilayer color films.

Referring now to FIG. 2 of the drawings, there is represented an opticalviewing apparatus for evaluating a reconnaissance film, such as atransparency F' printed from a negative exposed by the camera of FIG. 1and including multiple images of a common scene which have exposed toseparate zones of the actinic electromagnetic spectrum. Consideringfirst the evaluation of the positive transparencies by a monochromepresentation of individual spectral positives, which may be the visibleparts of the spectrum red, green, blue, for detailed study of thecharacteristics in each band, the apparatus of FIG. 2 includes meanssuch as a plurality of white light sources 23-26 for illuminating filmimages individually with white lights.

To this end, the apparatus of FIG. 2 consists essentially of fourindividual projection systems which are arranged in a close verticalarray within an appropriate lens angle such that all of the projectedphotographs lie in accurate registration, forming a composite image 27on a viewing screen 28. To this end, blue, green, red, and infraredphoto images or transparencies 29-32 on the same film strip F' are fedinto the object plane of projection lenses 46-49 and illuminated by thecondensing lenses 33-36, being accurately positioned by means of atransparent backing plate 37 and a closely spaced transparent frontplate 38. The lower edge of the film F' engages a reference surface 39which is in the same relative position to the film strip F' as thereference surface 20 to the film negative F in the camera of FIG. 1. Aroller 40, indexed by a light spring 41, engages the upper edge of thefilm F' to maintain the lower edge in alignment with the referencessurfaces 39.

The transparencies 29-32 are illuminated by the light sources 23-26 viabeam splitters such as half-silvered mirrors 42-45, respectively, whichreflect the light from the sources 23-26 onto the transparencies throughthe condensing lenses 33-36. The condensing lenses 33-36 illuminate thetransparencies 29-32 at the object planes of projection lenses 46-49,respectively, which, in turn, project the images in superposed relationto form the composite image 27 on the viewing screen 28.

Slight misregistration of the several images in the vertical directionat the viewing screen 28, due to differential shrinkage along the filmwidth, may be compensated by vertically adjusting the positions of theprojection lenses 46-49 by means of mechanisms indicated schematicallyat 50-53, respectively. The registration adjustments may be observeddirectly in the image 27 on the viewing screen 28. Further to assist insecuring accurate registration of the component images in the compositeimage 27, index marks such as the marks 54-57 are placed on the filmstrip F in the camera during exposure and reproduced on the positivefilm F' adjacent the respective images 29-32. Any small registrationcorrections required may be effected by rotating the film guide 37-38-39slightly in the X-Y plane by a mechanism not shown.

In order to provide for interpretation and evaluation of the projectedzones of the actinic electromagnetic spectrum such as red, green, blue,and infrared images individually or in any selected combination, theoptical viewing apparatus of FIG. 2 includes means for selectivelymaking effective any one or more, for example a selected pluality, ofthe illuminating sources 23-26. This means may take the form of a seriesof manually operated switches 58-61, respectively, connected to energizethe light sources from suitable supply terminals 62 through adjustableresistors 63-66, respectively.

The optical viewing apparatus of FIG. 2 further comprises means foraltering the relative intensities of illumination of the images formedby the light sources 23-26. This adjustment of illumination in intensitymay be, in part, effected by the adjustable resistors 63-66, butpreferably is effected by a plurality of graduated-density filters 67-70individually disposed in operative relation to the light sources 23-26,respectively. Each of the filters 67-70 comprises a series of discretestandardized neutral density wedges by means of which the illuminationof the images can be varied in predetermined steps. The filters 67-70are shown in strip form mounted between feed spools 71-74 and takeupspools 75-78, respectively, which spools may be wound and unwound byconventional means not shown.

For conventional multispectral analysis, each spectral-zonal image isviewed individually by selectively closing the switches 58-61, theoperator making note of the achromatic tonal characteristics peculiar toan area of interest. In this mode for example, the red spectral-zonalimage 31 may be analyzed by closing switch 60, energizing light source25, which illuminates the image 31 via the beam splitter 44 and thecondensing lens 35. The image 31 thus illuminated is projected onto theviewing screen 28 by means of the projector lens 48. In a similarmanner, the individual green and blue spectral-zonal images may beanalyzed, in turn, by selective operation of the switches 58 and 59,respectively, energizing the light sources 23 and 24.

A standard black-and-white camouflage detection is available bydeenergizing all light sources 23-25 and closing switch 61 to energizethe light source 26. The resultant image of 32 on screen 28 represents,in this particular example, the radiation emitted from the scene in theinfrared spectral zone.

A conventional black-and-white display, similar to that of apanchromatic photograph, can be obtained by the addition of thespectral-zonal images 29-31 by energizing the light sources 23-25through their respective switches 58-60. The zonal images 29-31 are thenprojected through their respective lenses 46-48 onto the screen 28. Byaligning the fiducial marks 54-56 and adjusting the projection lenses46-48, as described above, the images on the screen 28 of the threespectral-zonal film images 29-31 may be brought into accurateregistration at the screen 28. The resulting image is similar to thattaken by a single lens camera using a panchromatic film. By adjustingthe neutral density film strips 67-69 adjacent the light sources 23-25,respectively, the brightness of the individual spectral-zonal images29-31 may be varied selectively without changing the color temperatureof the lamps. The neutral density strips 67-70 may comprise a series ofdiscrete portions with incremental density variations of 0.05.

The optical viewing apparatus of FIG. 2 also includes provisions forevaluating the images 29-31 in true color or false color. To this end,there are provided means for illuminating the film images 29-31individually with lights through filters of substantially the samechromaticities as the original filters in the camera or, alternatively,with lights through filters of chromaticities substantially differentfrom the original filters in the camera. This means comprises aplurality of light sources 80-83 and a plurality of spectral filtersassociated therewith such as the red, green, and blue filter groups84-87, respectively, the order of the red, green, and blue filters inthe several groups being transposed from group to group. These filtersare individually mounted adjacent to the light sources 80-83 and, in onemode of operation, have transmission characteristics substantially thesame as th taking filters of the images 29-31, respectively. It shouldbe noted that no infrared filter is used in projection since infraredradiation is not visible to the operator looking at viewing screen 28.Filter belts 84-87 are movably mounted so that, by selectivelytranslating the various filters, the filter associated with any givenspectral-zonal image will have a transmission characteristic of the samechromaticity as the taking filter in the camera or one differingtherefrom.

The optical viewing apparatus of FIG. 2 further comprises means formaking effective to a desired degree any one or more, for example aselected plurality, of the light sources 80-83. This includes means foraltering the relative intensities of illumination of the images 29-32without altering their relative chromaticities, for example, a pluralityof neutral density filters 92-95 individually disposed adjacent thelight sources 80-83, respectively. These filters may be of the samegeneral type as the neutral density filters 67-70, successive discreteportions thereof varying in density by increments of 0.05.

The apparatus further comprises means for individually adjusting thefilters relative to the light sources to alter the relative intensitiesof the illumination of the images 29-32. This adjustment may be made bymounting the filters 92-95 on feed spools 96-99 and takeup spools100-103, respectively. The images 29-32 can be selectively illuminatedsingly or in desired combinations by energizing the light sources 80-83from the supply terminal 62 through manually operable switches 104-107,respectively, via adjustable resistors 108-111, respectively. Theresistors 108-111 may be used to adjust the relative intensity ofillumination of the several images 29-32, but preferably these are usedfor set-up purposes to ensure equal illuminations under referenceconditions and the illumination of the several images for evaluation isvaried by adjustment of the neutral density filters 92-95.

In making a true color evaluation of a scene, the light sources 80-82are energized by closing their respective switches 104-106, the lightfrom the sources 80-82 passing through the neutral density filters 92-94and the color filters 84-86, respectively. For true color evaluation,the neutral density filters 92-94 are adjusted for equal attenuation.The light from the sources 80-82 passes through the beam splitters42-44, the condensing lenses 33-35, the film images 29-31, and theprojection lenses 46-48, which combine them to form a composite truecolor image 27 on the screen 28 by conventional color addition. Theoverall color appearance of the composite image may be adjusted byselectively adjusting the neutral density filter strips 92-94, whichmodifies the relative intensities of illumination of the blue, green,and red images 29-31, respectively.

For example, in a scene which has been photographed at a reasonably lowsun angle, the surrounding terrain is cast in a pink or reddish color.By increasing the neutral density in front of the red filter 86, theamount of illumination on the red spectral image 31 is decreased and theresultant image on the screen can be made to appear in more naturalcolor balance. Any desired color balance may be achieved by appropriateselection of the neutral density filters in association with the severallight sources 80-82.

In some reconnaissance work, it is desired to project the spectral-zonalimages 29-32 in false colors. For example, by illuminating the red,green, and infrared spectral-zonal images 30, 31, and 32 with green,blue, and red illuminations, respectively, the resultant composite image27 on the viewing screen 28 will be a false color image. The shift indominant hue resulting from this transposition of the filters isnecessary because the infrared taking filter in the camera does nottransmit in the visible region of the electromagnetic spectrum. As intrue color presentation, the color camouflage detection images areilluminated at full saturation. However, for purposes of targetdetection, the several images may be selectively desaturated, asdescribed hereinafter.

As stated above, the spectral filters 84-87 associated with the lightsources 80--83 are readily interchangeable, not only for the purpose ofdisplaying false color, as described, but also to increase the abilityof the observer to detect small differences in chromaticity. Forexample, it is a known psychophysical fact that the noticeability ofchromatic differences is much more acute in the blue and red regions ofthe spectrum than in the green region. Therefore, if a given scene intrue color exhibits a predominant green hue, small chromatic differencesin the target and surrounding objects may not be detectable in a truecolor presentation. By interchanging the green and blue spectral filters84 and 85, the resulting composite image 27 will have a blue cast andexisting differences in chromaticities in the different areas of thescene are more readily discernible.

An example of the aid of transposition of colors is a camouflage-paintedvehicle. Such a camouflage-painted vehicle and cut foliage applied to itor surrounding it absorb infrared radiation while the living deciduousfoliage in the background reflects infrared radiation. Therefore, alarge image contrast between the target and its environment will existin the infrared spectral-zonal image. By projecting the infrared imageas red, the red image as green, and the green image as blue, a vividchromatic difference will occur in the composite image between thevehicle, its surrounding cut foliage, and the living deciduousbackground foliage. This color difference renders target recognitionmuch more reliable and much quicker than is possible by formerreconnaissance systems.

A completely saturated image does not always contribute to optimumevaluation of certain types of targets so that it is often advantageouspartially to desaturate the color representing certain major areas ofthe spectral zone, while maintaining the saturation of the areas ofinterest unaltered. This result may be achieved by simultaneously andselectively making effective any one or more of the white light sources23-26 and the chromatic light sources 80-83 by selective operation ofthe switches 58-61 and 104-107. The correct amount of desaturation ofany color is dependent upon the over-all scene brightness and thespectral reflectivity of the target as well as its surroundingenvironment. The amount of desaturation may be varied by adjusting theneutral density filters 67-70 adjacent to the white light sources 23-26,respectively.

A spectral-zonal color reconnaissance system embodying the invention hasa wide range of applications, among which may be mentioned the followingin which advantages are particularly realized:

1. Rapid screening of large volumes of reconnaissance data.

2. Camouflage detection.

3. Mine detection and location.

4. Bomb damage assessment.

5. Counter insurgency.

6. Image enhancement.

7. Airborne photo data reduction.

8. Geological reconnaissance.

9. Planimetric data compilation.

10. Detailed technical analysis of strategic targets.

11. Crop analysis.

12. Rescue operations.

13. Parachute drop support.

14. Antisubmarine warfare.

15. Ocean surveillance.

16. Oceanographic research.

17. Forest survey.

18. Biological, chemical warfare.

19. Land use surveys.

20. Amphibious reconnaissance.

21. Battlefield surveillance for change detection.

22. Semi-automatic photo interpretation.

While there has been described what is, at present, considered to be thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein, without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

I claim:
 1. A method of remote sensing comprising the steps offorming aplurality of photographic images of a common scene overflown by anairplane or satellite or the like by exposure of different film portionsrespectively primarily to different zones of the actinic electromagneticspectrum; developing said images; illuminating the several developedfilm images individually with lights of selected chromaticities, thechromaticity of the light illuminating at least one of said developedimages being substantially different from the chromaticity associatedwith the corresponding exposing spectral zone for that image;simultaneously displaying the illuminated developed images inregistration for evaluation; and individually varying the brightness ofthe contributions of the several developed images to the displayresulting in contrasts, (of differences), from which information aboutthe scene may be easily discerned.
 2. A method according to claim 1comprising the further step of individually varying the saturation ofthe contributions of the several developed images to the display.
 3. Amethod according to claim 1 wherein all of said images are formed on asingle strip of film in precise relative positions with respect to eachother and with respect to the film, whereby the display of theilluminated developed images in registration is facilitated.
 4. A methodaccording to claim 1 further comprising the steps of forming all of saidimages on a single strip of film in precise relative positions withrespect to each other, and indexing the film strip during exposurethereof and also during the display of the illuminated developed imagesto reference positions, whereby the display of the illuminated developedimages in registration is facilitated.
 5. A method according to claim 1further comprising the steps of forming all of said images on a singlestrip of film in precise relative positions with respect to each other,and forming a plurality of index marks on the film in precise relativepositions with respect to said images, whereby the display of theilluminated developed images in registration is facilitated.
 6. In aremote sensing system, an optical viewing apparatus for evaluating areconnaissance film including multiple photographic images of a commonscene overflown by an airplane or satellite or the like, the imagesbeing respectively exposed primarily to separated zones of the actinicelectromagnetic spectrum comprising:means for illuminating the filmimages individually with white lights; additional means for illuminatingthe film images individually with lights of substantially the samechromaticities as their respective exposing spectra; means forselectively making effective any one or more of said illuminating means;means for individually varying the brightness of said lights; andoptical means for displaying the selected illuminated images forevaluation.
 7. In a remote sensing system, an optical viewing apparatusfor evaluating a reconnaissance film including multiple photographicimages of a common scene overflown by an airplane or satellite or thelike, the images being respectively exposed primarily to separated zonesof the actinic electromagnetic spectrum comprising:means forilluminating the film images individually with white lights; additionalmeans for illuminating the film images individually with lights ofsubstantially the same chromaticities as their respective exposingspectra; means for selectively making effective any one or more of saidwhite light illuminating means; means for selectively making effectiveany one or more of said chromatic illuminating means simultaneously withillumination by said white light illuminating means; means forindividually varying the brightness of said lights; and optical meansfor simultaneously displaying the selected illuminated images forevaluation. .Iadd.
 8. A method of remote sensing comprising the steps offorming at least four photographic images of a common scene overflown byan airplane or satellite or the like by exposure of different filmportions on a single strip of film in precise relative positions withrespect to each other respectively primarily to different zones of theactinic electromagnetic spectrum, at least one of the photographs beingin the non-visible region of said spectrum; developing said images;illuminating the said developed film images individually with lights ofselected chromaticities, each chromaticity selected being a portion ofthe visible spectrum and not white light, the chromaticity of the lightilluminating at least one of said developed images being substantiallydifferent from the chromaticity associated with the correspondingexposing spectral zone for that image; simultaneously displaying theilluminated developed images in registration for evaluation in anoptical viewing apparatus having at least four projection means, saidevaluation being based upon objectively measurable color; andindividually varying the brightness of the contributions of several ofthe developed images to the display resulting in contrasts (ordifferences) from which information about the scene may be easilydiscerned..Iaddend. .Iadd.9. A method of remote sensing comprising thesteps offorming at least four photographic images of a common sceneoverflown by an airplane or satellite or the like by exposure ofdifferent film portions respectively primarily to different zones of theactinic electromagnetic spectrum, at least one of the photographs beingin the non-visible region of said spectrum; developing said images;illuminating the said developed film images individually with lights ofselected chromaticities, each chromaticity selected being a portion ofthe visible spectrum and not white light, the chromaticity of the lightilluminating at least one of said developed images being substantiallydifferent from the chromaticity associated with the correspondingexposing spectral zone for that image; simultaneously displaying theilluminated developed images in registration for evaluation in anoptical viewing apparatus having at least four projection means, saidevaluation being based upon objectively measurable color; andindividually varying the brightness of the contributions of several ofthe developed images to the display resulting in contrasts (ofdifferences) from which information about the scene may be easilydiscerned. .Iaddend..Iadd.
 10. In a remote sensing system, an opticalviewing apparatus for evaluating a reconnaissance film including atleast four photographic images of a common scene overflown by anairplane or satellite or the like, the images being exposed primarily toseparated zones of the actinic electromagnetic spectrum comprising:means for illuminating the film images individually with white lights;additional means for simultaneously illuminating at least three of thefilm images individually with lights of substantially differentchromaticities from their respective exposing spectra, whichchromaticities are different portions of the visible spectrum; means forselectively making effective any one or more of said illuminating means;means for individually varying the brightness of said lights; andoptical means having at least four projection means for displaying theselected illuminated images for evaluation. .Iaddend.